In this article we distinguish two questions about judicial review. First, substance: what acts or decisions are properly subject to the grounds of review? Second, procedure: what acts or decisions are properly reviewable through the judicial review procedure? Then we settle both. Our answer to substance is that two principles determine the scope of the grounds of review, the first a principle of regularity, the second a principle of non‐arbitrariness. Our answer to procedure is that acts or decisions are amenable to judicial review when two conditions are met, the first that the grounds of review apply, the second that no alternative procedure adequately enforces those grounds.